ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus GmbHGöttingen, Germany10.5194/acp-11-12351-2011The influence of eruption season on the global aerosol evolution and radiative impact of tropical volcanic eruptionsTooheyM.13KrügerK.1NiemeierU.2TimmreckC.21Leibniz Institute of Marine Sciences (IFM-GEOMAR), Kiel, Germany2Max Planck Institute for Meteorology, Hamburg, Germany3Invited contribution by M. Toohey, recipient of the EGU Young Scientists' Outstanding Poster Presentation Award 20100912201111231235112367This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from http://www.atmos-chem-phys.net/11/12351/2011/acp-11-12351-2011.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/12351/2011/acp-11-12351-2011.pdf

Simulations of tropical volcanic eruptions using a general circulation model
with coupled aerosol microphysics are used to assess the influence of season
of eruption on the aerosol evolution and radiative impacts at the Earth's
surface. This analysis is presented for eruptions with SO<sub>2</sub> injection
magnitudes of 17 and 700 Tg, the former consistent with estimates of the
1991 Mt. Pinatubo eruption, the later a near-"super eruption". For each
eruption magnitude, simulations are performed with eruptions at
15° N, at four equally spaced times of year. Sensitivity to eruption
season of aerosol optical depth (AOD), clear-sky and all-sky shortwave (SW)
radiative flux is quantified by first integrating each field for four years
after the eruption, then calculating for each cumulative field the absolute
or percent difference between the maximum and minimum response from the four
eruption seasons. Eruption season has a significant influence on AOD and
clear-sky SW radiative flux anomalies for both eruption magnitudes. The
sensitivity to eruption season for both fields is generally weak in the
tropics, but increases in the mid- and high latitudes, reaching maximum
values of ~75 %. Global mean AOD and clear-sky SW anomalies show
sensitivity to eruption season on the order of 15–20 %, which results from
differences in aerosol effective radius for the different eruption seasons.
Smallest aerosol size and largest cumulative impact result from a January
eruption for Pinatubo-magnitude eruption, and from a July eruption for the
near-super eruption. In contrast to AOD and clear-sky SW anomalies, all-sky
SW anomalies are found to be insensitive to season of eruption for the
Pinatubo-magnitude eruption experiment, due to the reflection of solar
radiation by clouds in the mid- to high latitudes. However, differences in
all-sky SW anomalies between eruptions in different seasons are significant
for the larger eruption magnitude, and the ~15 % sensitivity to
eruption season of the global mean all-sky SW anomalies is comparable to the
sensitivity of global mean AOD and clear-sky SW anomalies. Our estimates of
sensitivity to eruption season are larger than previously reported estimates:
implications regarding volcanic AOD timeseries reconstructions and their use
in climate models are discussed.